Several constructs using the power of recombinant DNA technology were employed to express in eukaryotic vector systems the envelope genes encoded by the HTLV-III virus. One type of construct incoporates a portion of the HTLV-III envelope genes fused to an SV40 promoter region, complete with splice and polyadenylation signals. A second type of expression vector construct fused the HTLV-III viral envelope gene with the SV40 T antigen amino terminal region, which can elicit proteins recognized by specific antibodies directly against T antigen. Both types of constructs, after contransfection into TK- cells along with the thymidine kinase gene, gave rise to selective transformants that enabled permanent lines to be established. In particular, 8 out of 10 such cell lines were found to be expressing HTLV-III envelope specific mRNA. Four of these cell lines were expressing high levels of message, while the other four were moderately expressive. Recombinant vectors containing metallothionein promoter inducible HTLV-III envelope genes were recently constructed conatining SV40 T antigen splice and polyadenylation signals and are being introduced into embryonic mice for transgenic expression studies.